Process for producing balanced half tones



April 10, 1934.

F. T. POWERS 1,954,097

PROCESS FOR PRODUCING BALANCED HALF TONES Original Filed May 1, 1931INVENTOR .Patented Apr. 10, 19 34 PATENT OFFICE PROCESS FOR PRODUCINGBALANCED HALF TONES Frank T. Powers, Douglaston, N. Y.

Application May 1, 1931, Serial No. 534,343 Renewed October 12, 1933 4Claims.

My invention relates to the photo mechanical reproductive arts andparticularly to the making of tone balanced half tone plates and thecopying of pictures in the graphic and photographic 5 arts.

The object of the invention is to provide a rapid and labour savingprocess for making a reproduction of a picture or drawing, which shallhave the desired tone balance between high lights, middle tones and deepshadows, without the necessity of hand work or retouching by the artist.

In the art, as heretofore practised, it has been the custom, whencopying or making a half tone reproduction of a picture, to make anegative or half tone plate of the picture, and by careful work by askilled artist, to balance the high lights, middle tones and shadows tothe desired degree to produce the best effects by the manipulation ofvarious processes known to those skilled in this art.

Some of these processes, whereby such reproductions are improved by theartist, are intensification, re-etching, hand-tooling, printingwithmasks and double printing. The suc- 26 cess or effectiveness ofthese processes depends in very large degree upon the skill, experienceand artistic sense of the operator, and are slow and time-consuming, andsince the operators are very highly paid, the processes are expensive.

By the application of my invention a picture which, in the original ispoorly balanced, may be so reproduced that the high lights, middle tonesand deep shadows will have such relative values as the artist desires togive them to produce the most artistic eflect, without the slow, tedioushand, chemical and tool processes now relied upon to produce these muchdesired results.

In the commercial reproduction of pictures it is more often true thannot that the copy submitted to the reproduction process is lacking inwhat the photo-engraver calls balance. It may be what is called in theart on the high side or the low side of proper balance. The details maybe weak or indistinct in the high lights, or

the shadows may be too deep.

By exposing in a camera a light sensitive plate to such a picture for ashort time, a photograph may be obtained which contains all the detailsof the high lights, although the exposure has not been sufl'icient tobring out the middle tones or deep shadows with the desired distinctnessor detail. If, on the other hand, the exposure is made sufiicient to getall the detail of the darker portions of the picture, then the lighterareas will be over exposed and the depth and detail therein lost.

If a compromise is made in thetime of exposure in an attempt to avoidboth over exposure of the high lights and under exposure of the deepshadows, there results a reproduction which may be satisfactory in themiddle tones or lighter shadows, but which still leaves much to bedesired in both the high lights and the deep shadows.

To overcome this difiiculty, I have devised a as process which I carryout in the maner which I will now describe in such detail that oneskilled in the art to which it pertains may practise it.

In this description and in the succeeding claims,

I use the word design to mean any design, picture, painting, photograph,drawing or graph of any sort, which may be copied by this process.

In describing the various steps of my new process, it is assumed that adesign is being reproduced by the half tone process and that the designis unbalanced in that it has poorly defined detail in the shadows. Myfirst step is to photograph the design on any suitable medium, which maybe, for example, a dry plate, a wet plate, a cut film or a continuousfilm, or such film as is commonly 30 used in the moving pictureindustry.

In making the exposure of this first photograph of the design beingreproduced, I intentionally under-expose it, with the result that Ireproduce detail only in the high light portion 35 of the design. Thefiddle tones and deep shadows are so underexposed as to fail to getdetail therein.

My next step is to photograph the design in a manner exactly similar tothe step described above, except that the exposure is somewhat nearer tonormal exposure, with the result that somewhat greater detail will besecured in the darker tones.

I continue these steps of making photographs of the design andprogressively increasing the exposure until I reach a point where theentire design is over-exposed, even in the darker shadows.

One convenient method of taking this series of pictures of varyingexposures is to use a moving picture camera oi. suitable design and amoving picture film. By opening and closing an iris diaphragm in thelens of this camera, while a series of exposures of the design beingcopied is made, I produce a series of negatives, some of which areunder-exposed and some of which are overexposed, whlle others are ofmore nearly normal exposure. Those exposures which are made when thediaphragm is wide open will be overexposed and those made when theopening in the diaphragm is small will be under-exposed, while theintermediate exposures will range between.

these two extremes.

Thus I have a series of photographs of the design, which advance bysmall stages or increments of exposure from one which is greatlyunder-exposed to one which is greatly over-exposed. The number ofpictures in this series varies with different subjects and also with theeffects sought in the final reproduction. The number may be as few asthree, or it may be as many as several score, as is the case when movingpicture film is used in making the photographs, as is further describedherein.

This series of negatives is next printed on another light sensitiveplate or film to produce a series of positives. In making the positiveprints the exposure of each picture is identical with each otherexposure, so that the resulting positives form a series of pictureshaving characteristics ranging from under-exposure to over-exposure. Orif I desire a positive of the design on my final picture, I may omitthis last described step.

I next project, one after another, images of these pictures in registerwith each other, upon a suitable screen by means of a suitableprojector, and while so projected upon the screen I expose a lightsensitive medium in a suitable camera to the image on the screen. Infront of the light sensitive medium in the camera is interposed betweenit and the lens a half tone line plate of the type well known in theart, and commonly called a screen or line screen. It will be referred toin this description as a half tone line plate to avoid confusion withthe word screen which is herein used to denote a screen upon which thepictures are projected. While making the exposure of the light sensitivemedium to the image projected on the screen, I progressively throw uponthe screen, one after another, images of the series of pictures whichwere exposed various lengths of time to the original design, some ofwhich are under-exposed and some of which are over-exposed, and allintermediate degrees of exposure. In projecting these images upon thescreen, care must be taken to insure that each successive imageregisters'in the exact position on the screen with the previous image.Unless these images all register exactly with each other on the screen,the resulting half tone composite negative of these images will beblurred or lack sharpness of detail.

In the accompanying drawing, I have shown diagrammatically thearrangement of projector screen and camera as they are set up to carryout my new process.

When I use moving picture film, as described above, I may splice the twoends of the filmtogether to form a continuous loop, which may be placedin a moving picture projector and the series of pictures thrownrepeatedly upon the screen as many times as is desired. The result isthat the light sensitive medium in the camera is exposed successively toimages on the screen, which are of gradually increasing depth ordensity, and which impart the tones and details so much desired, butwhich in the past were only obtained with difilculty, if at all.

. By this process I capture on the photographic plate being exposed inthe camera, a composite picture containing all the detail and balancepossessed by any of the pictures in the series. For example, from theunder-exposed imageson the screen I secure detail in the high lights,while from the over-exposed images I secure detail in the shadows. Thus,by manipulating the exposures and so subjecting the half tone plate tothe various pictures of the series, I produce a well-balanced efiectwith greatly improved detail, and do it without the usual resort ortedious methods referred to above.

Having described my invention, I now state what I claim to be new andnovel and for which I pray that Letters Patent be granted.

I claim:

1. The process for producing tone balanced half tone negatives, whichconsists in preparing a series of negatives of the design to bereproduced, said series varying in successive, approximately equalsteps, from under-exposure to over-exposure, preparing positives of saidnegatives, projecting images of. said positives successively in registeron a screen and photographing through a half tone line plate on a singlelight sensitive medium the successive images to produce a composite halftone negative having balance between the high lights, shadows and halftones.

2. The process for producing tone balanced reproductions of a designwhich consists in preparing a progressive series of photographs of thedesign, some of said photographs being under-exposed, sorne normallexposed, and some over-exposed, projecting images of said photographs inregister on a screen and simultaneously exposing a light sensitivemedium in a camera to said images .to produce a reproduction havingbalance in the high lights, shadows and half tones.

3. The process for producing tone balanced reproductions of a designwhich consists in exposing successive portions of a continuous strip oflight sensitive medium in a suitable camera to the design, with changingdegrees of exposure, developing the pictures so produced, preparingpositives of said pictures, projecting the images of said positivepictures successively in register on a screen and simultaneouslyexposing through a half tone line plate a light sensitive medium in acamera to said images to produce a tone balanced, composite half tonenegative.

4. The process for producing tone balanced reproductions of a designwhich consists in exposing successive portions of a continuous strip oflight sensitive medium in a suitable camera to the design with changingdegrees of exposure, developing the pictures so produced, preparingpositives of said pictures on a continuous strip of light sensitivemedium, attaching the ends of the said strip of light sensitive mediumto form an endless strip, projecting images of said positive picturessuccessively in register on a suitable screen, and simultaneouslyexposing through a half tone line plate a light sensitive medium in acamera to said images to produce a tone balanced composite, half tonenegative.

FRANK T. POWERS.

